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NEW YORK - Five former aides to investment manager Bernard Madoff were convicted on Monday of charges that they helped their boss conceal his massive Ponzi scheme for years.

A federal jury in New York found back-office director Daniel Bonventre, portfolio managers Annette Bongiorno and Joann Crupi, and computer programmers Jerome O’Hara and George Perez guilty on all counts, including securities fraud and conspiracy to defraud clients.

The trial lasted more than five months.

Madoff was arrested in December 2008 for running a Ponzi scheme that is estimated to have cost investors more than $17 billion US of principal.

“These five defendants played crucial roles in constructing and maintaining the house of cards that was the Madoff investment fraud,” U.S. Attorney Preet Bharara said in a statement. “The scheme these defendants helped perpetrate cost innumerable investors their life savings. Now it likely will cost the defendants their freedom.”

Nine other people have pleaded guilty in connection with Madoff’s fraud. Madoff, 75, is serving a 150-year-prison sentence after pleading guilty in March 2009.

At the trial, prosecutors introduced as evidence thousands of pages of internal documents seized from Madoff’s investment firm and called dozens of witnesses.

Chief among the witnesses was Madoff’s right-hand man, Frank DiPascali, who implicated each of the five defendants in the fraud.

While there was little dispute that various defendants engaged in activities such as backdating fake trades and creating false documents, the case turned on whether they knew at the time that they were aiding Madoff’s fraud.

Bonventre and Bongiorno took the stand in their own defense and denied knowing there was a fraud at the time it was taking place.

The case is U.S. v. O’Hara et al, U.S. District Court, Southern District of New York, No. 10-cr-00228.